1. Field of the Invention
The present invention relates to the field of a radio telecommunication apparatus used in a radio telecommunication system, and more particularly to a radio telephone apparatus such as a cellular mobile telephone apparatus.
2. Description of the Related Art
In a conventional cellular mobile telephone system, a service area connected to a mobile telephone switching office is divided into a plurality of small zones or cells. A base station is provided for each cell and is connected to any cellular mobile telephone apparatus (hereinafter simply called mobile telephone apparatus) within the cell via a radio channel and connected to the mobile telephone switching office corresponding to the service area via a land line. The mobile telephone switching offices of a plurality of service areas are connected to telephone switching offices via land lines.
In order to use the mobile telephone service, a user must make a contact with a mobile telephone service company. When the user takes the telephone apparatus to a dealer of the mobile telephone service company, the serial number of the telephone apparatus is registered and a system identification (SID) number denoting a service area in which the user usually uses the telephone apparatus and an associated mobile identification (MID) number denoting the telephone number of the telephone apparatus are assigned to the telephone apparatus. These assigned ID numbers are stored in a read only memory (ROM) in the telephone apparatus by the dealer. Usually, a plurality of service areas are provided by the mobile telephone service company and a service fee is dependent on the location of the user. In order to determine the location of the user, the SID number stored in the ROM of the telephone apparatus is detected at the time of originating a call. The service area corresponding to the assigned SID number is called a "HOME" area and the user within the "HOME" area is called a home area user. The other service area is called a "ROAM" area and the user within the "ROAM" area is called a roamer. A user fee for a call from the roamer is higher than that from the home area user. When a call is made from a mobile telephone apparatus, these ID numbers are automatically transmitted to the mobile telephone switching office covering the service area where the mobile telephone apparatus is located and the mobile telephone switching office can therefore distinguish the roamer and the home area user by checking the transmitted SID number.
Accordingly, if the user travels out the "HOME" area and enters a new area, the user must take the telephone apparatus to the dealer to change the stored SID and MID numbers to new SID and MID numbers corresponding to the new area in order to avoid an unreasonable increase of the user fee. Since the aforementioned numbers are changed and rewritten into the ROM by the dealer, it takes a lot of time to make such a change and the user requires to have a troublesome work.
In order to avoid this troublesome work, it has been attempted to store pairs of the SID and MID numbers corresponding to all the service areas covered by the telephone company in the telephone apparatus. The user only select a suitable pair of the SID and MID numbers by means of a switch when he or she changes the location. In some situations, however, the user does not exactly know in which area he or she is presently located. Thus, the user sometimes cannot select the proper ID numbers. Further, it is necessary to require a memory of a considerably great capacity in order to store all the pairs of the SID and MID numbers. Therefore, a high product cost results.
Those problems described above are also involved in a case where the user makes respective contacts with several telephone companies.